[v5] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()
Commit Message
As comments in ftrace_process_locs(), there may be NULL pointers in
mcount_loc section:
> Some architecture linkers will pad between
> the different mcount_loc sections of different
> object files to satisfy alignments.
> Skip any NULL pointers.
After commit 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
NULL pointers will be accounted when allocating ftrace pages but skipped
before adding into ftrace pages, this may result in some pages not being
used. Then after commit 706c81f87f84 ("ftrace: Remove extra helper
functions"), warning may occur at:
WARN_ON(pg->next);
To fix it, only warn for case that no pointers skipped but pages not used
up, then free those unused pages after releasing ftrace_lock.
Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
Changes v4 [6] => v5:
- Extract page free logic in ftrace_allocate_pages() as ftrace_free_pages(),
then call it to free unused pages in ftrace_process_locs().
Changes v3 [3] => v4:
- Keep the upside-down-xmas-tree format as Steve suggested [5].
Changes v2 [2] => v3:
- Check NULL for 'pg->next' before assigning it to variable 'pg_unuse'.
Changes v1 [1] => v2:
- As Steve suggested [4], only warn for case that no pointers skipped
but pages not used up then free those unused pages. But I move
the free process after releasing ftrace_lock.
- Update commit messages about the new solution.
[1] https://lore.kernel.org/all/20230710212958.274126-1-zhengyejian1@huawei.com/
[2] https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/
[3] https://lore.kernel.org/all/20230711112752.2595316-1-zhengyejian1@huawei.com/
[4] https://lore.kernel.org/all/20230710104625.421c851a@gandalf.local.home/
[5] https://lore.kernel.org/all/20230711095802.71406422@gandalf.local.home/
[6] https://lore.kernel.org/all/20230712013103.3021978-1-zhengyejian1@huawei.com/
kernel/trace/ftrace.c | 45 +++++++++++++++++++++++++++++--------------
1 file changed, 31 insertions(+), 14 deletions(-)
Comments
On Wed, 12 Jul 2023 14:04:52 +0800
Zheng Yejian <zhengyejian1@huawei.com> wrote:
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -3305,6 +3305,22 @@ static int ftrace_allocate_records(struct ftrace_page *pg, int count)
> return cnt;
> }
>
> +static void ftrace_free_pages(struct ftrace_page *pages)
> +{
> + struct ftrace_page *pg = pages;
> +
> + while (pg) {
> + if (pg->records) {
> + free_pages((unsigned long)pg->records, pg->order);
> + ftrace_number_of_pages -= 1 << pg->order;
> + }
> + pages = pg->next;
> + kfree(pg);
> + pg = pages;
> + ftrace_number_of_groups--;
> + }
> +}
> +
> static struct ftrace_page *
> ftrace_allocate_pages(unsigned long num_to_init)
> {
> @@ -3343,17 +3359,7 @@ ftrace_allocate_pages(unsigned long num_to_init)
> return start_pg;
>
> free_pages:
> - pg = start_pg;
> - while (pg) {
> - if (pg->records) {
> - free_pages((unsigned long)pg->records, pg->order);
> - ftrace_number_of_pages -= 1 << pg->order;
> - }
> - start_pg = pg->next;
> - kfree(pg);
> - pg = start_pg;
> - ftrace_number_of_groups--;
> - }
> + ftrace_free_pages(start_pg);
> pr_info("ftrace: FAILED to allocate memory for functions\n");
> return NULL;
> }
Nice little clean up. I had already started testing your previous patch,
but due to my test machine running out of disk space (perf doesn't clean up
its .debug directory :-p), I have to rerun it.
I'll apply this one for the new testing.
Thanks!
-- Steve
@@ -3305,6 +3305,22 @@ static int ftrace_allocate_records(struct ftrace_page *pg, int count)
return cnt;
}
+static void ftrace_free_pages(struct ftrace_page *pages)
+{
+ struct ftrace_page *pg = pages;
+
+ while (pg) {
+ if (pg->records) {
+ free_pages((unsigned long)pg->records, pg->order);
+ ftrace_number_of_pages -= 1 << pg->order;
+ }
+ pages = pg->next;
+ kfree(pg);
+ pg = pages;
+ ftrace_number_of_groups--;
+ }
+}
+
static struct ftrace_page *
ftrace_allocate_pages(unsigned long num_to_init)
{
@@ -3343,17 +3359,7 @@ ftrace_allocate_pages(unsigned long num_to_init)
return start_pg;
free_pages:
- pg = start_pg;
- while (pg) {
- if (pg->records) {
- free_pages((unsigned long)pg->records, pg->order);
- ftrace_number_of_pages -= 1 << pg->order;
- }
- start_pg = pg->next;
- kfree(pg);
- pg = start_pg;
- ftrace_number_of_groups--;
- }
+ ftrace_free_pages(start_pg);
pr_info("ftrace: FAILED to allocate memory for functions\n");
return NULL;
}
@@ -6471,9 +6477,11 @@ static int ftrace_process_locs(struct module *mod,
unsigned long *start,
unsigned long *end)
{
+ struct ftrace_page *pg_unuse = NULL;
struct ftrace_page *start_pg;
struct ftrace_page *pg;
struct dyn_ftrace *rec;
+ unsigned long skipped = 0;
unsigned long count;
unsigned long *p;
unsigned long addr;
@@ -6536,8 +6544,10 @@ static int ftrace_process_locs(struct module *mod,
* object files to satisfy alignments.
* Skip any NULL pointers.
*/
- if (!addr)
+ if (!addr) {
+ skipped++;
continue;
+ }
end_offset = (pg->index+1) * sizeof(pg->records[0]);
if (end_offset > PAGE_SIZE << pg->order) {
@@ -6551,8 +6561,10 @@ static int ftrace_process_locs(struct module *mod,
rec->ip = addr;
}
- /* We should have used all pages */
- WARN_ON(pg->next);
+ if (pg->next) {
+ pg_unuse = pg->next;
+ pg->next = NULL;
+ }
/* Assign the last page to ftrace_pages */
ftrace_pages = pg;
@@ -6574,6 +6586,11 @@ static int ftrace_process_locs(struct module *mod,
out:
mutex_unlock(&ftrace_lock);
+ /* We should have used all pages unless we skipped some */
+ if (pg_unuse) {
+ WARN_ON(!skipped);
+ ftrace_free_pages(pg_unuse);
+ }
return ret;
}